The invention relates to an ignition system for an internal combustion engine.
In the case of non self-ignitable internal combustion engines, the fuel mixture is usually ignited by a spark plug in the combustion chambers of the internal combustion engine by means of which an ignition coil discharges itself.
In this process it is important that a sufficient amount of energy is accumulated in the ignition coil to be able to trigger the ignition spark that requires a correspondingly high electrical current through the ignition coil.
On the other hand, the electrical energy accumulated in the ignition coil should also not be too high because this leads to an increased thermal load of the ignition coil and the ignition output stage and furthermore wear of the spark plug.
Therefore, before each ignition process the electrical energy accumulated in the ignition coil should be within a specified bandwidth to allow the safe triggering of an ignition spark in the case of a minimum thermal load of the ignition coil and the ignition output stage and as little wear as possible of the spark plug.
Therefore, ignition output stages based on Darlington transistors that allow a current limitation are well-known, whereby the energy in the ignition coil is restricted.
However, a disadvantage of such current limiting ignition output stages is the fact that a great amount of heat dissipation is converted because of the current limitation in the ignition output stage.
An ignition system is well-known from DE 43 31 994 A1 in which the ignition output stage is activated via a bidirectional control line in which case the ignition output stage reports back the current value of the ignition coil current via the bidirectional control line. Similar ignition systems are well-known from DE 38 00 932 A1, W092/17702, DE 27 34 164 A1 and DE 28 21 062 A1.
Finally, an ignition system is well-known from EP 0 555 851 A2 in which the ignition output stage measures the ignition voltage and reports back via a separate line.
Therefore, the object of the invention is based on creating an ignition system for an internal combustion engine that allows a setting of the ignition energy or the ignition current that is as exact as possible without there being a great amount of heat dissipation. In this case, the possibility of a test should be created to determine whether or not the ignition energy was sufficient to trigger an ignition spark with as few connecting lines as possible.
This object can be achieved by an ignition system for an internal combustion engine comprising an output for electrical activation of an ignition element for a combustion chamber in an internal combustion engine, an electrical energy accumulator connected to the output for accumulating the electrical energy required for activating the ignition element, a controllable control element connected to the energy accumulator which is used to charge the energy accumulator during a predefined charge time, a measuring unit for detecting the charge state of the energy accumulator, wherein to set the charge time for the energy accumulator, a timer is provided, said timer being connected to the control element on the output side, and the measuring unit is connected to said timer in a feedback loop whereby the timer adjusts the charge time according to the measured charge state of the energy accumulator, and wherein the measuring unit and the control element, on the one hand, and the timer, on the other hand, are interconnected via a bidirectional control line, wherein the energy accumulator is connected to a voltage measurement unit that monitors the ignition voltage wherein the voltage measurement unit is connected to the control line on the output side via a controllable current source or a controllable current sink to superimpose a current signal on the control line according to the measured voltage.
The measuring unit may have a precision resistor that is connected in series to the energy accumulator. A threshold element can be arranged in the feedback loop between the measuring unit and the timer that compares the measured charge state of the energy accumulator with a predefined threshold value and generates a control signal for the timer according to the comparison. The measuring unit can be connected to the control line via a controllable current sink and/or a controllable current source to superimpose a current signal on the control line for feedback to the timer. The voltage measurement unit may comprise a comparator with two inlets between which the energy accumulator is connected, wherein the comparator activates the controllable current source or the controllable current sink when exceeding a predefined reference voltage value. The energy accumulator can be connected to the comparator via a protective resistor.
The object can also be achieved by a method for controlling the an ignition system for an internal combustion engine comprising the steps of:
charging an energy accumulator during a predefined charge time to accumulate electrical energy for providing an ignition voltage,
detecting the charge state of the energy accumulator,
setting the charge time for the energy accumulator by means of a timer via a bidirectional line, wherein the timer adjusts the charge time according to the measured charge state of the energy accumulator via said bidirectional line,
measuring the ignition voltage thereby superimposing a current signal on the bidirectional line according to the measured voltage.
The method may further comprise the step of comparing the measured charge state of the energy accumulator with a predefined threshold value and generating a control signal for the timer according to the comparison. The method may further comprise the step of superimposing a current signal on the bidirectional line for feedback to the timer. The current signal can be superimposed when the ignition voltage exceeds a predefined reference voltage value.
The invention includes the general technical theory of adjusting the charge time for the ignition coil instead of limiting the current, in which case the charge time is adjusted according to the electrical current at the end of the charge time.
Therefore, the ignition system according to the invention has a timer that sets the duration of the charge time and, therefore, the energy content of the ignition coil before the next ignition process.
The ignition system according to the invention also has a measuring unit for detecting the charge state of the energy accumulator in which case the measuring unit is connected to said timer in a feedback loop to adjust the charge time according to the charge state that is set at the end of the charge time.
If the energy content at the end of the charge time is too low to trigger an ignition spark, the charge time is adjusted upwards by the feedback loop so that the energy content of the ignition coil is increased during the next charge process. For this, the switch-on time of the control element connected to the ignition coil is tilted forwards, whereas the switch-off time and, with that the end of the charge process are retained because this time is predefined by the time of ignition according to the specific crankshaft setting.
However, if the measuring unit detects that the energy content of the ignition coil at the end of the charge time is higher than necessary, the charge time is adjusted downwards by the feedback loop while the switch-on time of the control element connected to the energy accumulator is shifted backwards in which case the charge time is reduced. However, the switch-off time and thereby the end of the charge time are retained in this case since this time is specified by the predefined ignition point.
The measuring unit preferably has a precision resistor for measuring the charge state that is connected in series to the energy accumulator or the ignition coil so that the electrical voltage dropping via the precision resistor allows the energy content of the ignition coil to be determined.
A threshold element is preferably arranged in the feedback loop between the measuring unit and the timer that compares the measured charge state of the energy accumulator with a predefined threshold value and generates a control signal for the timer according to the comparison. Therefore, in this embodiment only one digital signal is transferred via the feedback loop that indicates whether or not the charge time is too long or too short.
In the preferred embodiment of the invention the data is transmitted via a bidirectional control line between the timer and the measuring unit, on the one hand, and the controllable control element, on the other hand. The data is preferably transmitted here from the measuring unit to the timer in such a way that the measuring unit activates a controllable current sink or a controllable current source to superimpose a current signal on the bidirectional control line for feedback to the timer.
A voltmeter is also connected to the energy accumulator that monitors the ignition voltage in which case the voltmeter is connected to the bidirectional control line on the output side via a controllable current source or a controllable current sink to superimpose a current signal on the control line according to the measured voltage. In this way, information about the duration of the ignition spark can be transferred to the timer.